MP2155 –HIGH EFFICIENCY SINGLE INDUCTOR BUCK-BOOST CONVERTER WITH 2.2A SWITCHES

MP2155 Rev. 1.0

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1/26/2014

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waveforms the current may be much lower than

this value when SWD is turned off because of

internal delay.

SCP/OCP vs. two current limits

There are two current limits in MP2155. The

primary one is for steady PWM operation and it’s

typically from 2A to 3A, depending on Vin; The

secondary one is for limiting inrush current at

startup, it’s typically 1.6A to 1.9A, depending on

Vin, too. When load is over heavy, the primary

limit would protect MP2155 from being over

thermal. Therefore Vout would drop due to OCP.

If Vout drops below 0.6 times normal output, a

hiccup period is initiated to protect MP2155. this

is the SCP. In hiccup period, SWA and SWC are

turned off while SWB and SWD are turned on.

After the hiccup period ends, a soft re-startup

begins. Because Vout is below 1V (due to over

load or output short), the secondary current takes

charge of this process. After Vo rises above 1V,

primary current limit get in charge of. Now if load

is still over heavy (or output short still exists)

such that after SS ends Vout is still below

another hiccup period begins. However if the

load recovers to normal value during re-startup

so that current doesn’t hit its limit, or, Vout

startup succeeds, and MP2155 enter normal

operation.

As to the input/EN startup, the cases are same

as the SCP recovery process.

Enable

The MP2155 has a dedicated enable control pin

(EN). The device operates when it is set high. If it

is set low the device stops switching, all the

internal blocks are turned off. Tie EN to Vin

through a resistor for automatic start up. Due to

EN bias or leakage current, the value of this

resistor should be set to provide EN pin with a

current above 10uA. Any signal to drive this pin

should be limited to 100uA if the maximum

voltage of this signal is above 6.5V.

Internal Soft-start

When EN pin is pulled high, and at the same time

the voltage on Vcc pin is above its UVLO rising

threshold MP2155 will start up with Soft-start

function to eliminate output overshoot. Soft-start

also functions during SCP recovery.

Under-Voltage Lockout

The under voltage lockout (UVLO) is implement

to protect the device from improper operating at

insufficient supply voltage. When the supply

voltage at VCC is below the UVLO threshold the

device is in shutdown mode. The UVLO rising

threshold is about 1.8V with 200mV hysteresis.

Over-Temperature Protection

An internal temperature sensor continuously

monitors the IC junction temperature. If the IC

temperature exceeds 160ºC typically the device

stops operating. As soon as the temperature falls

below 140 ºC typically normal operation is

restored.